The present invention relates to systems for monitoring tires. More particularly, it concerns the processing of measurements carried out on tires in order to give one or more alarms.
Numerous arrangements, such as that of U.S. Pat. No. 4,703,650, have been proposed in order to transmit inflation pressure measurements of each tire continuously to a central unit, accompanied possibly by measurements of the temperature of the air within the tires.
However, a knowledge of the inflation pressures is not sufficient to provide the driver with reliable, useful information. The continuous consulting of these indications runs the risk of being more tedious than actually useful. As a matter of fact, the pressure and/or temperature measurements of tires vary enormously upon travel due to the heating of the tires as a result of hysteresis losses, the influence of the heat given off by the brakes, and transfers of load which cause slight variations in the volume of the tires.
For this reason, U.S. Pat. No. 4,893,110 has proposed a method of processing measurements based on comparisons between two or more tires, directed at the ability to give off an alarm in case of a leak of a tire without adopting alarm thresholds which are too far from the precision attained by the measurement devices.
This processing, despite its interest, has not completely solved the problem. In fact, the improvement in the precision of the detection in case of leak of a tire requires that the initial pressures of the tires be strictly identical. Actually, this is by no means the case and it is entirely customary and usual to observe differences in inflation pressure when cold on the order of 10% or even 15%. This is furthermore the range accepted, for instance, by the European Technical Rim and Tire Organization (ETRTO) for heavy vehicles. These differences are due in particular to the precision of about 5% of the inflation gauges, the lack of precision upon inflation of about 3%, the consequences of sunshine on one of the tires, etc. The method described in the aforementioned application can therefore not have a better precision of detection than the customary initial differences, if one does not desire to bring about numerous false alarms. Therefore, a leak in one of the tires can be detected only after a very substantial decrease in the inflation pressure of the tire and one which makes immediate repair necessary.